A circuitbreaker pole part can be integrated in a medium-voltage to high-voltage circuitbreaker arrangement. For example, medium-voltage circuitbreakers are rated between 1 and 72 kV of a high current level. These specific breakers interrupt the current by creating and extinguishing the arc in a vacuum container. Inside the vacuum container a pair of corresponding electrical switching contacts is accommodated. Modern vacuum circuitbreakers can have a longer life expectancy than former air circuitbreakers. Although, vacuum circuitbreakers can replace aircircuit breakers, the present disclosure is not only applicable to vacuum circuitbreakers but also for air circuitbreakers or modern SF6 circuitbreakers having a chamber filled with sulfurhexafluoride gas instead of vacuum. For actuating a circuitbreaker, a drive with a high force is used which moves one of the electrical contacts of a vacuum interrupter insert for a purpose of electrical power interruption. Therefore, a mechanical connection between a drive and an axially movable electrical contact inside the vacuum interrupter insert is provided.
The document WO 2012/007172 A1 discloses a circuit breaker pole part having an external insulating sleeve made of a solid synthetic material for supporting and housing a vacuum interrupter insert for electrical switching a medium-voltage circuit, wherein an adhesive material layer is applied at least on the lateral area of the interrupter insert. The coated interrupter insert is embedded by molding with the solid synthetic material (e.g., epoxy material, thermal plastic material, silicon rubber material). Thus, an intermediate layer with a mechanical compensating function and an adhesive property function for embedding the vacuum interrupter is provided. The special adhesive material layer according to this solution could be used for a temperature over at least 115° C. and could withstand −40° C. Due to ohmic losses in the pole parts and due to the limited heat transfer from the pole part to the environment, the temperature can increase during operation. Depending on the material used, certain maximum temperatures—which are defined in the relevant standards—are not to be exceeded. One of the most important regions of switching poles is the transition from the fixed parts to the movable parts.
Two known ways to increase a related nominal current of a pole part without increasing temperature are as follows. Firstly, the electrical resistance of the electrical contacts inside the vacuum interrupter insert could be reduced by increasing the cross-section of the electrical contacts which can be made of a copper material. However, this solution will increase the material effort. Secondly, the heat transfer can be improved since there can be regions on a pole part where the allowed temperatures are fully exploited while in other regions there is still a margin.
The document DE 41 42 971 A1 discloses a pole part for a medium-voltage circuitbreaker having an insulation housing with an upper electrical terminal and a lower electrical terminal for electrically connecting the pole part with a medium-voltage circuit. A vacuum interrupter insert is integrated in the insulation housing and its fixed upper electrical contact is electrically connected to the upper electrical terminal; its movable lower electrical contact is electrically connected to the lower electrical terminal.
Inside the vacuum interrupter insert a ring-shaped shield is integrated surrounding the area of both electrical switching contacts. The shield can be formed of metallic or ceramic material. The shield is used as a thermal protection shield in order to avoid critical temperatures in the area of the electrical switching contacts only.